I like my Sierra-1s very much; I bought them used and at the time the center had been upgraded to the NrT tweeter; later I added the NrTs to the L/R as well; no slouches either way by the way. If I were to buy Sierras now (and am now more into diy), I'd get Sierra-2s with the Raal tweeter (if not suck it up and get Horizons/Sierra Towers

). The 340s may be a bit better in a larger room, tho.
I was thinking more of the long term and possibility of larger rooms down the line with the 340s vs 170s, too.
Philmarmonic was brought up, too and getting the Affordable Accuracy speakers for your size room would be a great way to get good sound and save some money (I have BR-1 kit that speaker is based on, plus some crossovers for them I bought from Dennis for a diy version from scratch). If you can afford other Philharmonics, that's a definite option. Dennis doesn't have the in home trial programs like SVS or Ascend offers as far as I'm aware, though....