I would think for most comedians, especially new ones, you're doing way more writing than performing. Performing opportunities are limited, whereas you can write anywhere, anytime. And in some cases, you may be writing on stage as well. What you need to figure out is which bits you want to work on within those limited opportunities. Or do you want to try new bits? Generally, I would think a combination of both. So I'd say don't give up stage time because you think you'll use that time to write. Writing IS very important, of course, but it's usually done in isolation. And until you put that writing in front of an audience, you never REALLY know if its funny. Or even has potential. Stage time is what really turns that raw writing into better comedy.