Unlike skiing, I'm not seeing an option at destinations for renting higher performance gear.
If you're like, ahem, 'some' of us, and there's more than one 'x' in your XL sizing on some things, odds of the rental fleet having your size is iffy.
That said, there's something about the notion with rental gear, the airline won't get a chance to lose it in transit, and it won't arrive late (a hassle at a land-based destination; downright awful if you're boarding a live-aboard the day of arrival).
So, what's high performance? The priciest gear is apt to be your computer and regulator (assuming you're not real picky about BCD; some would be), and those things fit in your carry on anyway. Wetsuits are bulky but need to fit; are you an average size and not too chubby? Mask fit is rare enough for some people that many are well-advised to take their own mask. If you like downloading computer dives to your home computer, what are the odds that rental computers do that? If the computer's not going home with you, are you packing a notebook to download to?
I like my own mask and computer. I like my 2XL OMS slipstream and XL Atomic Smoke-on-the-Water fins, size 13-14 (still not quite big enough; I wear a 15) boots or the size 15 boots, 2XL Sherwood Avid BCD, 2XL Henderson AquaLock hood (largest they make and stretchy material yet still pulls on my lower jaw unpleasantly) and Henderson 2XL 5 mm gloves. I'm not an easy mask seal person. My 3XL Henderson Thermoprene wetsuit fits snug but okay since the material is so stretchy, the 4XL shorty is comfy, and I'm not lean.
Basically, I'm not a guy you want showing up fearless at a foreign dive shop saying 'Okay, gear me up.' And while my dimensions/needs aren't average, there are a lot of people who overlap me in one more more areas. How many threads do we see snide references to seeing obese divers on boat trips? How many wetsuits over 2XL do you see in rental offerings? Especially 4 or 5 XL?
Richard.