buying boat for PHRF racing
First off PHRF ratings vary from region to region so the numbers that I ma quoting may not be the same in your area.
There are a number of different ways to approach finding a boat to race PHRF with a rating of 170 or above. One way is to look for an older one design race boat. Boats like the J-24 (174), J-22 or Kirby 25 (171-174) can be purchased fairly reasonably and generally can be sailed to their rating. Because these are race boats much is know about the design of their sails and proper tuning procedures. These have minimal interior comforts but they are fun to sail and are quiet fast which makes it especially easy to save your time in light air or a dying breeze.
Another way to go is with a cruiser/racer. Boats like the Catalina 27 (204), and Pearson 30 (180) are reasonably fast boats which also have reasonable interiors. These are still raced one design and so tuning info is available. They do require some upgrades from a stock boat to make them competitive but you can often buy an optomized and competitive boat for a reasonable price.
Then there are old MORC boats. These seem to be reasonably competitive. A good example might be the Lindenberg 26 (180) which in the right hands is a very fast boat.
Another way to go is to buy a reasonably quick boat that is not thought of as a race boat. Since few of them are raced in an optomized form they can have very competitive ratings. Two boats that come to mind here is the Irwin Citation 30 (171-183) and the Hunter 30 (177-180). Both these boats are primarily bought as cruisers by cruisers and so have pretty generous PHRF ratings. Neither were all that well built and may have other problems associated with them but they can be made into pretty competitive PHRF boats. My dad raced owned and raced a 1981 Hunter 30. He did some optomization, better sails and deck hardware,and went club racing for several years without finishing any lower than a first or second place. They lowered his rating several times totalling 12 seconds a mile and he still did very well. What was interesting in his case is that other Hunter 30 owners complained that the rating changes were too extreme and the rating was actually raised by 3 secs so the net change was only 8 secs. If you go that route look for deep keel -tall rig versions of the Irwin as they are much faster than their shoal draft, short rig sisters. In the case of the Hunter 30 the shoal keel is less of a penalty but the tall rig is still a good idea.
Then there are boats that are just good sailing boats like the Ranger 23 and 26, or Santana 235 and 525''s.
Good luck with your campaign.