That's not as simple a question as it first appears.
Here're two things to consider performance wise...
1) How large is the file to download
2) How hard is it to process?
To be honest... if you care about performance, make your pages XHTML instead of HTML. In capable browsers that's your best performance. Don't get scared by the X, it's basically HTML with some stricter rules, if you know HTML it'll take you about 5 minutes to learn XHTML.
Those closing HTML tags do in fact make the file a tiny bit larger, but they make the browser work ALOT less to render the page.
FrontPage does annoying other things, like add in bunches and bunches of "formatting code". My favorite, I had three full lines defining font types, colors, sizes etc... to format a . Those things do slow it down.
So basically to answer your question... the performance is hurt significantly by FP, but with DSL and a 1GHz+ processor, you're not really going to notice on 90% of pages.
-Rob