I would not bother with the Transformer T100 if you are looking for a primary laptop. If you were looking for a lightweight supplemental laptop in addition to your current laptop / desktop, then perhaps it would do. But not as a primary workhorse.
The Bay Trail generation Atom CPU is pretty powerful compared to the prior generation Clover Trail generation Atom CPU, but it has nowhere near the power of a dual core i3 CPU. The small 10.1" 1366x768 resolution screen is not very good for large spreadsheets. In addition, it has a small keyboard which may or may not be an issue.
There is also no way to expand on the integrated 2GB of RAM. That is all you get. The 2GB of RAM will limit what you can do.
If the Toshiba Kirabook fits your needs, then go for it. 12.5" to 13.3" laptops are generally expensive because they combine both lightweight and relatively powerful performance. You should also be aware that you are not getting a quad core i7 CPU. Mobile Core i7 CPUs comes in two flavors dual core and quad core. In order for a lightweight laptop to qualify as an "ultrabook" it must have a ULV (ultra low voltage) CPU with a TDP of probably no more than 17w. This is to keep power consumption down so that the ultrabook will have longer battery life and also reduced heat because a lightweight laptop means a relatively light heatsink used to cool the CPU.
"U" model Intel CPU are dual core CPUs like the i7-3637U used in that Toshiba ultrabook and are up to 17w TDP. "M" model core i7 CPUs are also dual core CPUs that are rated at up to 37w. Quad core i7 mobile CPUs have the "MQ", "HQ" and "MX" designations. Their TDPs range between 37w and 57w.
The i5-3337u and i7-3637u CPUs are actually the prior generation Ivy Bridge CPUs not the current generation CPUs. Click the below link to help you determine if it is worth spend the extra money on the Core i7 CPU:
http
/ark.intel.com/compare/72055,72054