I don't think I've ever gone the minify route with X/HTML.
It's ugly, harder to maintain and of limited benefit.
I don't know any details of your web site. I find a good fast server, compiling the programmed bits and good attention to code design can give lightning speed.
If it's just markup a good fast server still applies. (I've had ISP's move web sites to alternate shared machines to achieve this.)
Working on images is always a good idea and can make a difference. (Note: it's not always the same format that gives you best results, gif, png and jpeg all have their place in the sun.) I'd put that ahead of minification.
I know that some smart people set things up to compress the payload from the server. (gzip) There used to be some problems doing that but I believe it's now much better. I imagine that will also outperform minification.
For a discussion of this issue I found http://stackoverflow.com/questions/728260/html-minification