Coming from a Jetski background, I may have more to add to this conversation.
1st off, I hear folks are having issues with getting replacement heads from Speedster. You can send your head off to Jim Holiday in Cartersville GA to be re-lathed and re-sized. Jim knows all about how to re-shape for different sized dome requirements, squish band, and the like. All you'll need to do is send him a head and give him squish clearance, angle, and required dome CC volume and he should be able to help you out for a very reasonable price. Call Jim at 770-386-6510.
2nd, CR or Compression Ratio is the actual figure you are trying to meet, not PSI. While pros very well may have figured out max PSI (Which is easily measured on a gauge) of 160 PSI for pump gas, or ~190 for ~110 octane, your actual calculated CR measurements are what it takes to fully calculate your CR, and ultimately your fuel requirements. Pump gas shouldn't run over about 11.5:1 CR. Race gas can go much higher (like 14:1 or even 16:1). CR is also affected by over-boring your cylinder of course.
3rd - cooling. The issue here with land-vehicles is over-all cooling capacity. See, with my jetski, I have an infinite amount of ~ambient temperature water around my craft, and so I can run 15:1 CR (220PSI) on 108/112 octane and still have the cyl/head stay at 150F. You can help by increasing cooling any way you can - bigger radiator/fan, water lines, pumps, cooling passages. One thing found with jet skis is if the water is flowing too fast through the head then the head actually gets hotter, and so restricting some flows give the head a better chance at heat transfer and allow the head to run cooler.
4th - Tuning.
Engine compression does not have very much impact on tuning, meaning an Engine at 140psi would very likely have the same jetting specs at as it would at 160psi, if only the head was changed out for one with smaller CC/dome. This makes tuning your Engine easier, as you can tune at a safer compression first before running the higher more detrimental compressions.
5th - at the end of the day, many race jetski-ers had found that lower Engine compression actually yields more power on the top-end - which is important for us land vehicles where often we are rung-out much the same. This has a bit to do with stresses added and heat-soak from the higher compression, EGT, pipe temps, and more. In the jetski world, we generally run much higher compression engines for requirements of bottom end hit (Like for stunts) which don't have much time to heat-soak, and lower compressions for free ride and race crafts (Top end pro-longed speeds).
6th - Run VP fuel like C12 or VP110 in your machine if you can. There are benefits from the lead additive which arguably can add lubricity to a 2-stroke - which is a nice if you believe it. Also since we're not running the machines every day the cost of the race fuel ($8-$14/gallon) doesn't really hurt that much in the grand terms of things. Especially if you have a local pump somewhere - just do it, but also plan on never going back to pump fuel again (Tune and what-not).
7th - Timing. With race fuel, bump the timing (Not sure if this can be done statically at the stator?) The calculation is about 1/8" per 4 degrees of timing - outter rim of the stator. Bumping the timing is something which usually goes hand-in-hand with introducing race fuel to things.
8th - Any Engine porting, specifically around lowering or raising your exhaust ports, affects cylinder port timing, relating to CR, and ultimately what fuel should be run. Expect a modified cylinder specifically around the tops of exhaust and transfer ports to be totally different than for a stock cylinder.
9th - I mentioned SQUISH band, or SQUISH Clearance as it is so called. On jetskis, we run minimum of 35thou clearance on race fuel for freestyle (Bottom-end) but upwards of 50-60 thousandths for to Mid/Top and race boats. Squish needs to be measured and is EASY!!! Two sticks of solder down the plug hole parallel to the crank shaft with the solder up against the cylinder wall side, then carefully turn the Engine past TDC (Top Dead Center) by hand. Mic the 'squished' solder and there you have your squish clearance in-hand. If your squish is too tight, it will severely throw off your compression readings on the gauge! Also could be cause of piston-edge over-heat, preignition, and detonation. I'd think our machines would need to run quite loose in this regard (Maybe 50 or greater squish?) Does anybody know what is the ideal squish?
10th - Gaskets. A thin or thick or lack of a Cylinder base gasket changes port timing and squish band. Port timing changes CR and octane requirements, and squish is well a static thing which you need to aim for. If the base gasket is thinner/thicker than stock, MEASURE YOUR SQUISH (#9). Cylinder head gaskets change your squish clearance only. The same thing goes if you've ever had your cylinder or head decked. MEASURE YOUR SQUISH.