Based on what you stated, I would go for a nice road bike with clip-on aero bars. Only put the aero bars on when doing tris or specific training rides by yourself. Group rides generally frown on aero bars as you tend to be a bit "twitchy" and can take out a lot of riders in a crash. My skin can attest to that. If you find yourself doing more tris in the future and have more disposal cash, add a tri-bike to the stable.
Alternatively, you can get a tri bike for racing and training and use the cyclocross bike for group rides. Speaking as someone who's done both, it's a lot easier to put road tires on a cyclocross bike than it is to change a road bike over from road to proper aero configuration. Bolting aero bars to a road bike will reduce your frontal area, which helps, but if you want to maintain a comfortable hip angle you will have to move your seat forward. That causes the aforementioned "twitchy" handling, which isn't a result of aero position per se, but rather of having too much weight over your front (steering) tire while you're bent over the bars. (Properly fitted tri bikes are extremely stable when ridden in the aero position since they generally have longer front centers than comparably sized road bikes - resulting in better weight distribution in the aero position). The other disadvantage of a converted road bike, particularly on hilly courses, is that you'll constantly have to reach from the aerobars to the drop bar mounted shifters to change gears. It doesn't sound like a major issue, but every time you reach for the shifter you disrupt your aerodynamics as well as your pedaling rhythm. My experience when I was riding a converted road bike was that I tended to grind over hills to avoid reaching for the shifter. When I finally got my first tri bike I was amazed both at how comfortable and relaxed I was in the aero position, and how much more efficient my riding became when the shifters were readily accessible.
In the end its going to come down to your judgment as to what you want most out of your new bike. If you plan to do mostly group riding, and especially if you're considering road racing (which is great training), you should get a road bike. If you think you're primarily going to use it for triathlon and solo training rides, you may be happier with a tri bike. And in the end, whichever one you don't buy this year you're going to buy next year anyway.
Have fun shopping.
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