I have couple of the 2700K SST-20 in a light. It’s a very nice color. You can get a rough idea of what the different color temperatures of light look like in person before buying a light. 2700K looks like the standard 40 watt incandescent in color. 4000K looks more like most older LED street lights or office lighting in color. 3500K has the stock fluorescent color. Both 3500K and 4000K are pretty common in office and retail fluorescent lighting with 3500K looking a bit “warmer” or closer to a halogen white.

As others have explained the 7135 is essentially the linear driver count. The greater number of linear regulators, expressed as 7135x6,7135x8, and so on, dictate how much power will be pushing the emitter. A 7135x6 driver is not a bad place to start. The user controls have gotten much better with Biscotti in these new lights, so you’ll be getting a much better deal in that regards.