Sounds like you got a decent deal as long as the brifters are in good working condition. You might want to remove the hoods (they cost about $55 a pair for new ones), and hose out the old lubricant (if the original Shimano lubricant hasn't been washed out already) with PB Blaster, and relubricate with a light synthetic grease. The original grease gums up with age, and makes the brifters get sticky or stop working. Don't let the spray get on the hoods, I think that's one of the reasons that hoods get sticky, the solvent in the spray reacts negatively with the rubber.

The only issues that I have with the RSX group is the way that Shimano used stickers to put the model name on the group parts (I think RX100, Ultegra, and 105 were paint), and what I consider to be the ugly appearance of the brake calipers. The brake calipers seem to work fine, but to my eye they look clunky when compared to RX100 A550 or Ultegra 6400, or 105 1055 dual pivot calipers.

Since you've written that you spin out the 14T on your old 6-speed freewheel occasionally, I'd think you might want to try one with an 11T since your top cog in now a 46T. Freewheels don't cost that much, so if it turns out to be too tall, you can always buy one with a lower top cog later. Check the chain before putting it on the bike, you don't want to cause excessive wear to the freewheel and chainrings. A new KMC chain (with a reusable link) will only cost you $6-$11, depending on which 6,7,8 speed compatible model you pick from eBay. A KMC master (missing link) will cost you $3-$4 alone from most LBS. You can order extra links from a eBay Seller for about $1.10 each.