I did play some ladder years back, then went away from the game entirely. Returning now has been painful, mostly because I just can not play at the level I played back then. Actually, I think there has been some rating deflation while I was away. I see players now doing stuff that was reserved for quite a bit higher rated players back then.
Even after trying to shake off the rust for a while, I am still far from my previous level. In custom games, with some many other players involved, my rating does not get easily adjusted, and in many cases people will yell at me for underperforming. In 1v1, which the question was about, I always feel it is hopeless. Judging by how many points I am losing per one ladder game, I will have to try, and lose, a truly depressing amount of games for the system to adapt.
Regarding map size: I am surprised to read that many of you hate the 5km maps. When I was better, I had no problem with them. They were like fast food: pleasurable and quickly consumed. I was somewhat better on larger maps though.
Now, 5km maps are my best chance. I will cap the core mexes, build a couple of factories, set rally points and send the commander straight through the middle. In a few minutes someone is going to explode. By reducing the game to this simplified situation, the effect of the skill gap is minimized. I admit that if I get a larger map, I will be tempted to just press alt+f4.
Reading more of the replies, I remembered one thing that I would like to add:
Get rid the big rocks and wrecks that you should be manually reclaiming. What they do is to make the game more BO dependent.