Pretty sure that neither of them have any reinforcement around the slide stop area
zoom in on the two listings here:
https://eagle6.co.uk/shop/catalog/product/view/id/1573/s/tokyo-marui-p226-r-top-slide-for-p226-gas-blowback-pistol-series/
https://eagle6.co.uk/shop/catalog/product/view/id/2801/s/tokyo-marui-p226e2-top-slide-for-p226-gas-blowback-pistol-series/
Without having either in front of me I'd have to defer to knowledge of current owners, there is always the option of an aftermarket slide/slide and frame kit.
The E2 model was "better" because the mags were improved and it had better gas efficiency. Much like yourself I prefer the size of the P226R, standard practice is to run them on E2 mags.