Andy,
Go on, go for the Basia, you know it makes sense. Shop around and you should beat £285 by a few bob.
Also consider the TS6000, a good £100 less than the Basia. The spool length and diameter are similar (identical ?) to the Basia, but deeper, so holds a lot more line (more than enough for anybody), the downside is the weight in comparison with the Basia.
With respect to the Basia spool capacity, you may be able to purchase alternative spools if you deal direct with a Japanese retailer.
Will,
There is no doubt that the Shimano reels are well built and engineered, but they don't have a monopoly on that concept. I just feel they are the wrong shape for outright distance. In simple words for fixed spool distance casting "long and thin" is better than "short and fat".