The Ilford Product Availability List (link to the PAL's PDF at:
http://www.ilfordphoto.com/products/page.asp?n=11) only lists one type of Warmtone paper: MGIV WT in RC and fibre versions (MGIV-RC WT and MGIV-FB WT).
Is there a typo in the first line of your post and you are asking for comparisons between normal MGIV (which comes in a white box and is ISO P500) and MGIV Warmtone (brown box, P200)?
If so, apart from the obvious differences in the emulsions, the Warmtone has a slightly off-white/cream base compared to the brilliant white of standard MGIV. I've not run a densitometer over the Warmtone so can't say re' Dmax but I expect Dmin will not be as good because of the paper base tone (it's nowhere near as creamy as the Kentmere Warmtone paper however).
Cheers, Bob.