MJ, the 9.5” size medium deep tart pan from Gobel is the one that Rose recommends for the Gateau Breton. It has a six cup capacity and can be filled about 2/3 full with most of Rose’s cake recipes- the cake will dome and rise up a little higher than the edge, but then shrink a bit on cooling and end up flat and full height. It doesn’t end up being a very tall cake, as max layer height is 1.25-1.375 “. I love it, but just wanted you to have full disclosure before taking the plunge.
A 9.5” tart pan is also the most frequently used size for tarts in the Pie-Pastry Bible, though there are other sizes required, too. The PPB uses the shorter 1” height x 9.5” tart pans, but so far I haven’t had any problems with the taller 1.375” pan. The only issue I can see for pies or tarts is that if you like to have the crust extend up and over the rim of the pan you might need to increase the quanity of pastry crust to give a larger circle. If you don’t extend up and over the rim, you have less chance of over-browning the crust, but also more shrinking down of the sides.
If you are using another author’s recipe and it calls for a 9” tart pan, you might want to increase the recipe to accomodate the larger diameter, but if it were me I wouldn’t do anything to account for the higher sides, as a deeper layer of pie filling often runs into problems. To increase the tart recipe from a 9” to a 9.5”, you would increase by 11.4%, or 10% would probably work just as well and be easier to calculate. It’s possible that you could skip the adjusments and make a thinner tart, but I don’t know if that would always work.
You might also check Amazon and/or a general web search to see who has the best price, as several vendors carry it.