COM likes to do things in large chunks because the roundtrip (cross process/ cross machine) is expensive. 100 per second might be OK. I think the last time I benched it, I was able to get up to ~1000 calls per second. But my memory may be wrong in this case. I certainly wouldn't try going much beyond 100, at least on a single core system.

The other thing to consider is [hosting the 1.1 CLR]. That is, within your Maya Plugin DLL, you host a CLR domain, and your managed code runs within this isolated environment. Kind of like adding a scripting engine, but the 'scripts' are your managed code.