In good wood, I like a light plane more, but there seems to be a lower limit for me with smoothers, except of the continental design. That's all just my opinion.
I'd call good wood something like clean straight soft maple, cherry, walnut, or - if one is lucky enough, mahogany. Beech sort of fits in there, too, especially the face of quartered boards.
I work cherry more than anything else, just because of where I am, i can get it any time FAS rough for 5 bucks a board foot and sometimes half or third of that. For working from rough, I like either the stanley or a woody jointer (I seem to be more accurate with a metal jointer if I'm trying to hit a tight mark, but you have to remember to wax it while you're working because it's easy to get tired and start to lean on it).
this answer's going nowhere fast. I guess it depends. If I could only have three planes, I'd have a japanese jack, a stanley 7 sized metal vintage plane and a stanley 4. But I'd rather at least have the option of having a wooden jointer or try plane at least 22" long and a vintage wooden jack - double iron both of them. Something in the 7 pound range for a long plane seems to be ideal for medium hardwoods, smoothers in the range of 3 1/2 to 4, and something around 5 for a jack.
I have noticed in the past that when I'm getting tired, the jtbrown plane will start to seem heavy when I pick it up off of an edge, but part of that's probably because it's long. It can remove wood fast.
If the wood is not so great, which is what I'd consider hard maple or stuff with lots of runout that comes right back into you on the opposite end of the board, it's nice to have heavier metal planes for everything but the coarsest work (the modern planes do have a little more accurate cap irons, too - a stanley 7 and 4 are definitely easier to set dead on where you want them). The infill kit/panel plane is like magic on really hard wood, but my experience is dampened with it a little because shepherd did a crap job with a capital C on making the cap iron and the iron - they are inaccurately made AND the iron is poor quality, delivering unexpected chipout at the edge often.
I tend to think after using all of them that the stanley 4 sold gobs for a reason, that the stanley 7 sold gobs for a reason, and the woody jointers were carefully made to the weights they are (They wouldn't have needed to keep all of that weight in front of and behind the iron in the non-razee planes if they didn't want to).
If you have a sore shoulder or back, a plane that doesn't get jarred in the cut seems all the more important. Sometimes I have mild arthritis, and the more ideal the plane, the less I notice it. I don't really like the idea of stopping physical work when woodworking is about all the physical work I get these days.