I've cut holes through my boats hulls before trying to get the most out of transducers and have found in most cases the simple external bracket works fine.
I would not recommend the 1kw transducers unless you like telling everyone you have a big one that cost more
I fish for deep water fish using big electric reels with 1500m of line and 5kg sinkers, mostly in water 300-1000m deep. I ran both lowrances standard 200/50htz and airmars tm260 and found the much cheaper Lowrance sounder was consistently better.
I tried talking two of my mates from buying the tm260, one for Lowrance and the other for furono. Both regretted it and like me have since sold them on ebay.
What depth are you wanting to sound as I can read bottom even up to 300m at 40kmh on 200htz and much deeper on 50htz at lower speeds (from a $200 transducer) external bracket mount.