The real question in deciding what size puzzle to attempt is whether you have enough good theme material to get to a Sunday-size puzzle. If you have a theme that you think is good enough for NYT Sunday, by all means go for it. There are a number of constructors who made their NYT debut on Sunday. I agree with you that there is a lot of variability in the NYT Sunday, both in difficulty and overall quality (whatever that is), but the one thing all NYT Sunday puzzles have in common is a theme that you can almost never say "I've seen this one before". Will is always looking for new twists, new ideas . . . you get the picture. Good luck!