Subscribes from bigger youtubers don't really make a difference - likes would help if they have it set up in their account to post it out,
I have mine set up so that if I comment on a video it puts it in to my feed, so I space it out that I only comment on my the days I don't upload to knock them back up my feed, haha you have to be careful not to post too much stuff to your subscribers and make it count lol
Also when I comment on a video it posts it on my facebook and twitter haha. - it's a good way to get two chances to hit your subs, you never get as many views on a new video as you have subs, only a small percentage. I get about 10k-25k views from a new video (first week of upload) out of those 71k
You're doing gaming videos so I'd aim to collab with gamers that have, I'd say shooting for twice as many subs. - Try to make it as easy as possible for the collab to actually happen - pitch an idea for a video and how it would work, I think just reaching out and asking 'do you want to collab?' will be quite vague and mean that they have to imagine how it would happen when they're answering that question... so if you can come up with a concept and explain that when you ask, you're helping them envision how it would work