Bike should have chain guard and long fenders to keep your ass and back dry and with mud flaps to keep your feet dry(ish). Might be a good idea to use rain boots and keep shoes in a bag if it's raining.
I definitely miss not having chain guard and fenders with Seattle weather, but have switched over to a raincoat and boots for biking. Waterproofing the commute is totally worth it.
Technology might have improved since I bought my last soft shell pant, though.
This past year I've been walking instead of cycling since it's more exercise.
http://www.motorcycle-superstore.com/36/i/firstgear-thermo-o...
The raincape/poncho, however dorky people may view it, is actually one of the more effective wet weather items provided it's not too windy.
My point was moreso that any sort of rainproof gear will eventually cause you to sweat due to decreased venting, and it's about finding the balance between sweating, or getting rained on. Everyone's mileage will obivously differ given different bodies, air humidities, and length of commute.
If it's raining, assume you have to change clothes. Any DWR-coated clothing will eventually wear off by the end of a season or two. And your shoes and socks will be the wettest items anyways.
Also during rain, there's a fine line between getting soaked from the rain, or sweating out from your rain jacket. Showers Pass has made bike-focused rain gear for a while that has plenty of reflective details and options for venting. Your basic rain jacket from TNF, Marmot, Patagucci will work in a pinch, too.
For moderate weather, plenty of companies have been (or used to be) targeted for bike-commuting: Swrve, Makers & Riders, and Outlier (the last one has moved away). They all offer stretchy pants made with synthetics so they dry quicker. Newer wool slacks with a touch of spandex from your typical big box retailers like Banana Republic also work because they're slightly stretchy and breathable. You'll probably wear them out faster, though, since wool doesn't handle abrasion that well.
But yeah, depending on the weather, how easily you sweat, and how far you have to ride, you may need a second set of clothes. Hopefully your office doesn't have a hoteling setup.