is 38/16 too low
 

is it?

if you are not riding riding faster then 20km/h then 38/16 is almost to high.

46/16 is good for flat. Just switch out the chainring.

I ride a 42-16 out here and it's hilly as ****.

Seems kinda low for my tastes, but i ride 47/16. One thing i noticed about my ratio is that things like doing hills or stop and go was a pain, but you get over that in a few weeks. Going for path rides or longer/higher avg speed rides is way easier, for obvious reasons. I've found that having more gear inches tends to help with things like riding green lights/moving with traffic across town with less effort, whereas fewer gear inches tends to burn me out faster (moreso even than dealing with stop and go).
Unless you live in the hills, you may want to step it up a bit, maybe keep a 14 in the back when you switch to fixed at first, then adjust after a few weeks if you run into problems... if you're riding a front brake, you'll hardly notice the difference after the first two or three days. In fact, you're probably going to feel like you need a bigger chainring.

Assuming 700x23c wheels, 38x16 requires a cadence of ~70 at 20km/h.

maybe you could try and get a smaller chainring

39 x 16 here. It's pretty sweet.

I have a 29er SS mountain bike with 34 X 20. It took a bit of pedaling, but on tuesday I overtook a FG cyclist that was pacing me for a while (he had a Bianchi Pista) with much higher gearing, downtown. I still don't understand how that's possible... but there you go. Maybe because Helsinki is a bit hilly.

I took that bike because it's the only to currently have fenders, and I didn't want mud on my azz.

I find 44 x 16 fine for 15 mph headwinds or for climbing a 2% grade slope, for 0.85 miles (or both). If you've ever crossed the Dumbarton Bride by bike you know what I am talking about.

38/16 is only in the low 60's (about 62 gear inches?). That seems way too low, unless you're in a really hilly area.
Try about 70 gear inches. Nice, happy medium. Personally, I mash 77.

i'm at 48/17 freewheeling now and it's murder going up hills (southern orange county is pretty freaking hilly) so i'm switching to 42/16 fixed 42/17 free. that's going to take me from 75 gear inches down to 66.

if it's flat where you are i'm thinking you're going to want something a little harder... but you really should just try it yourself because everyone's different.