Yep, I went with the Shimano CS-M771 cassette. It was on sale for less than the equivalent SRAM (PG-1070). I didn't even notice that SRAM doesn't make an 11-34!

I wanted 11-34 so I could have a 1:1 low gear with my 50/34 crank.

Yes, SRAM and Shimano use the same cog spacing for their cassettes. Even though Shimano calls their CX-M771 a "DynaSys" cassette, in reality there is no such thing. DynaSys uses the exact same cog spacing, just a different cable pull ratio.

SRAM's medium cage 10s road RDs (also called "WiFli", a dumb name) are rated to a 32t cog. Mine does fine with the 34t, but the upper pulley is really close to the cassette at that point.

Your SRAM Apex shifters are 10-speed, correct? SRAM's 10-speed MTB and Road RDs use the same cable pull ratio (Exact Actuation), so they're cross-compatible.
You could use a medium-cage SRAM 10s MTB rear derailleur instead of the mid-cage road (WiFli) RD, and that RD would fully support a 34t or even 36t big cog.
One big advantage of using a SRAM MTB RD is the clutch (aka "Type 2"). The clutch on the lower cage really helps to prevent chain slap on rough terrain (but it is a tiny bit heavier).

Unfortunately, SRAM changed the cable pull ratio for 11-speed MTB (X-Actuation), so their 11-speed MTB and Road stuff isn't cross-compatible anymore.
But, you could use a 10-speed SRAM MTB RD (Exact-Actuation) with 11-speed SRAM Road shifters (Exact-Actuation) for an 11-speed cassette.

$40 shipped is a great price on the XT cassette. I'd grab one (and maybe even a spare) at that price.

The HG-500 will be a bit heavier because less of its cogs are mounted to aluminum carriers (aka "spiders"). Those spiders reduce the amount of steel in the cassette (lower weight) and don't dig into alloy freehub bodies quite as badly as loose steel cogs do.