index build faster on 8G laptop than 30G server

I've been running an index build for almost an hour on my 30G server
that takes ~ 20 mins on my puny old macbook.

It seems like I've tuned all I can.. what am I missing?

Thanks,
Bill

Records to index: 33305041

--- Server:

PostgreSQL 9.2.15 on x86_64-redhat-linux-gnu, compiled by gcc (GCC)
4.8.3 20140
911 (Red Hat 4.8.3-9), 64-bit

shared_buffers = 8GB # min 128kB
temp_buffers = 2GB # min 800kB
work_mem = 8GB # min 64kB
checkpoint_segments = 256 # in logfile segments, min 1, 16MB each
seq_page_cost = 1.0 # measured on an arbitrary scale
random_page_cost = 1.0 # same scale as above
effective_cache_size = 20GB

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
4069 ec2-user 20 0 8596m 1.7g 1.7g R 99.8 5.6 67:48.36 postgres

Macbook:
PostgreSQL 9.4.4 on x86_64-apple-darwin14.3.0, compiled by Apple LLVM
version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn), 64-bit

shared_buffers = 2048MB # min 128kB
temp_buffers = 32MB # min 800kB
work_mem = 8MB # min 64kB
dynamic_shared_memory_type = posix # the default is the first option
checkpoint_segments = 32 # in logfile segments, min 1, 16MB each

PID COMMAND %CPU TIME #TH #WQ #PORTS MEM PURG CMPRS PGRP
52883 postgres 91.0 02:16:14 1/1 0 7 1427M+ 0B 622M- 52883