a 6 or 7

I use my #6 a lot, but for leveling a full size workbench or table, I'd go with a #7 or #8. For the way I work, I need both. (well, I like having both)

I only have up to a size 6 (Fore Plane aka Try Plane).

I'm sure the 7 (Jointer plane) Junkies will extol the virtues of 4 extra inches, but really it's in the hands of the user. Saying this 'cause I'm just jealous I don't have a 7??? Could be, but I don't think so. I've always done good enough with my Fore Plane.

Well it would depend on what you really want. If you don't mind it not being perfectly flat a 6 would be fine. The longer the plane the flatter you can get it, assuming you can use the plane correctly. You can pick up some transitional planes that were up to 30" long. That would make to where you at least had 30" sections of your project dead flat, but that is a little extreme and those monsters are hard to come by.

There are a few things to consider, but the 7 will be quicker than the 6. Of course, an 8 would be quicker than a 7. Bear in mind that, as a general rule, the bigger the plane, the bigger the price tag and the heavier it will be to push. The longer planes will also get you a flatter surface. Check with Don W to see what he has for sale. If he can't help you, drop me a note. I have a (ahem) few planes. Another thing to consider is that you don't need a Bedrock or Lie-Nielsen. You can get very, very good results with Stanley/Bailey, Millers Falls, Union, Sargent and a few others. The biggest thing is being able to sharpen and adjust the plane properly.

My plane arsenal ranges from a #2 to #7 and i find that most work will be much smaller than a large bench or table top. I have a 6 inch power joiner and I find it useful to flatten a board wider than that with a hand plane. My go to plane most of the time is a #6 and the more I us it the more uses I find for it. My #7 I use much less and mostly to flatten glued up panels wider than 24 inches. If i were to flatten a work bench I would be looking for a heavy #8. Going down the slippery slope you will probably end up with both but the #6 (which is not popular) to me is like the #5 but more useful.