I owned a GST and also recenlty purchased the new Executive seasonal 'grained calfskin' and I MUST tell you that the executive is considerably heavier than the GST. It is so heavy that I do not use it as an everyday bag, plus the only comfortable option due to the weight would be shoulder carry, however this is awkward as the straps are not quite long enough for it to be comfortable.
I strongly urge you to reconsider the GST if you are worried about the weight.
Regards the different leather, the grained calfskin (nubuck like leather) will not be as durable, after using my bag for only 1 week and only carrying my wallet, phone, keys and make up pouch, it was already sagging drastically.
It looks beautiful but for me it is no where near as practical as a day bag as my GST. If only using for work or travel then its probably okay but not everyday! Don't make the expensive mistake I did! $4,240 AUD later and I could have used that money a lot more wisely.
In Australia they are much more readily available. Like mentioned above I own the new seasonal grained calfskin and I will tell you now, after using it for a week the shape is no where near as structured as the one with classic calfskin that my mother owns.
If you are worried about it losing shape please reconsider the classic one, not grained calfskin! I feel like I was slightly 'tricked' by my SA who is the store manager, the bag definitely does not hold its shape and it is crazy heavy!!!
I can tell you after visiting the Chadstone boutique in Melbourne Australia, they have two regular size cerf totes with the classic calfskin, they are part of the classic, permanent collection, it just depends on whether they have them in stock as they are not as readily available as other classic line items.
The seasonal bag is also larger, much more practical as a work bag, the classic is slightly smaller in all dimensions (even strap length) as I compared them today after purchasing my seasonal grained calfskin roughly a month ago.
Just to clarify, the seasonal is the grained calfskin with ONLY SHW and the classic normal calfskin is with either.
Hope this helps and happy Chanel shopping!