Turbo R has the same waitstates in z80 mode. In R800 mode there are also added waitstates for memory refresh, but not as many and the amount depends on the amount of memory. A 512k tR is therefore a bit slower than a 256k version. Fun thing is, that the 1MB has actually the same speed as a 256k tR. Probably because the extension implements much of the mapper logic itself.