I'm thinking that there will be several different variables here, like what year your boat is and the style of the dash, your budget, brand that you want to go with and so forth. I don't have a 205 Tournament, though I do have a 228 Seafarer and bought a Garmin 943xsv last summer, which is a 9" touchscreen unit, and I think it works perfectly on my boat. On an even smaller boat like yours, I think a 9"-10" screen would be plenty big, and something that's 12" and above would very likely be overkill. I'd measure the area you're referring to, maybe even get the dimensions of what you're considering buying, cut out a template with cardboard or similar and see if it's about the size range you're looking for. As stated, I think a 12" display will be overkill, I think even something like that on a bigger boat like mine, would likely even be a bit overkill, and I'm a big proponent of utilizing two smaller sized screens over one larger one anyway. Another thing that you could do is go into your local West Marine or marine shop, see what they have and go from there. Everyone has different preferences for brand, I prefer Garmin because of how simple and easy they are to use, and they have all the features that I need with them. I'm sure others will be along shortly to chime in, but that's my opinion on the matter.